Apparatus and method for gaseous emissions treatment using front end induction heating

ABSTRACT

An assembly for treating gaseous emissions includes a substrate body having a front and a rear and cells for the passage of emissions gas. Inductance heating metal is located in the substrate body and an induction heating coil is mounted adjacent the substrate body for generating a varying electromagnetic field for inductively heating the metal and thereby heating the substrate body. A greater concentration of the metal is located near the front of the substrate body than near the rear.

CROSS REFERENCE TO RELATED PATENTS

The present application claims priority pursuant to 35 U.S.C. 119(e)from:

-   U.S. Provisional Application Ser. No. 62/234,166 filed Sep. 29, 2015    entitled “Catalytic converter structures with directed induction    heating”;-   U.S. Provisional Application Ser. No. 62/258,071 filed Nov. 20, 2015    entitled “Catalytic converter system with controlled induction    heating and methods for use”;-   U.S. Provisional Application Ser. No. 62/306,885 filed Mar. 11, 2016    entitled “Structures for inductive heating”;-   U.S. Provisional Application Ser. No. 62/322,719 filed Apr. 14, 2016    entitled “Induction heating structures”;

The present application is a continuation in part of U.S. patentapplication Ser. No. 14/452,800 entitled “Catalytic converter structureswith induction heating” filed Aug. 6, 2014 which claims prioritypursuant to 35 U.S.C. 119(e) from

-   U.S. Provisional Application Ser. No. 61/879,211 entitled “Catalytic    converter employing electrohydrodynamic technology” filed Sep. 18,    2013, and-   U.S. Provisional Application Ser. No. 61/910,067 entitled “Catalytic    converter employing electrohydrodynamic technology” filed Nov. 28,    2013.

The disclosures of the above-numbered applications are herebyincorporated herein by reference in their entirety and made part of thepresent application for all purposes.

This application is one of four related applications filed on the samedate and naming the inventors of this application, the relatedapplications being:

-   -   Apparatus and method for gaseous emissions treatment with        directed induction heating    -   Apparatus and method for gaseous emissions treatment using front        end induction heating    -   Apparatus and method for gaseous emissions treatment with        induction heating of loop conductors    -   Apparatus and method for gaseous emissions treatment with        enhanced catalyst distribution

FIELD OF THE INVENTION

This invention relates to a structures and methods of operation ofcatalytic converters, particulate filters (PFs) and like structures fortreating exhaust gases to reduce harmful pollution and has particularbut not exclusive application to reducing pollution from internalcombustion engines at start-up and when idling.

BACKGROUND

The U.S. Department of Transportation (DOT) and the U.S. EnvironmentalProtection Agency (EPA) have established U.S. federal rules that setnational greenhouse gas emission standards. Beginning with 2012 modelyear vehicles, automobile manufacturers required that fleet-widegreenhouse gas emissions be reduced by approximately five percent everyyear. Included in the requirements, for example, the new standardsdecreed that new passenger cars, light-duty trucks, and medium-dutypassenger vehicles had to have an estimated combined average emissionslevel no greater than 250 grams of carbon dioxide (CO₂) per mile invehicle model year 2016.

Catalytic converters and DPFs are used in internal combustion engines toreduce noxious exhaust emissions arising when fuel is burned as part ofthe combustion cycle. Significant among such emissions are carbonmonoxide and nitric oxide. These gases are dangerous to health but canbe converted to less noxious gases by oxidation respectively to carbondioxide and nitrogen/oxygen. Other noxious gaseous emission products,including unburned hydrocarbons, can also be converted either byoxidation or reduction to less noxious forms. The conversion processescan be effected or accelerated if they are performed at high temperatureand in the presence of a suitable catalyst being matched to theparticular noxious emission gas that is to be processed and converted toa benign gaseous form. For example, typical catalysts for the conversionof carbon monoxide to carbon dioxide are finely divided platinum andpalladium, while a typical catalyst for the conversion of nitric oxideto nitrogen and oxygen is finely divided rhodium.

Catalytic converters and PFs have low efficiency when cold, i.e. therunning temperature from ambient air start-up temperature to atemperature of the order of 300 C or “light-off” temperature, being thetemperature where the metal catalyst starts to accelerate the pollutantconversion processes previously described. Light-off is oftencharacterized as the temperature at which a 50% reduction in toxicemissions occurs and for gasoline is approximately 300° C. Belowlight-off temperature, little to no catalytic action takes place. Thisis therefore the period during a vehicle's daily use during which mostof the vehicle's polluting emissions are produced. Getting the catalyticconverter or PF hot as quickly as possible is important to reducing coldstart emissions.

Copending U.S. patent application Ser. No. 14/452,800 (Catalyticconverter structures with induction heating) shows a catalytic converterassembly having a substrate body with a plurality of cells for celltherethrough of exhaust gases. Metal is located at predeterminedlocations in the substrate body and an electromagnetic field generatoris mounted adjacent the substrate body for generating a varyingelectromagnetic field inductively to heat the metal and so heat thesubstrate body.

SUMMARY OF THE INVENTION

According to one aspect of the invention, an assembly for treatinggaseous emissions comprises a substrate body having a plurality of cellsfor the passage of emissions gas, respective lengths of metal wirelocated in each of a first set of the plurality of cells, and aninduction heating coil mounted adjacent the substrate body forgenerating a varying electromagnetic field, thereby inductively to heatthe lengths of wire and thereby to heat the substrate body, wherein thewires are distributed non-uniformly through the substrate body to obtaina desired inductance heating pattern at the substrate body.

In one implementation, a relatively higher concentration of the wiresper unit volume is sited towards the center of the substrate body tocompensate for the fact that electromagnetic flux generated by theinduction heating coil center falls off with distance from the coil. Inanother implementation, cells in regions radially remote from the centerof the substrate body contain little or no wires so that electromagneticflux generated at the coil is not absorbed within these regions but,instead, penetrates more deeply towards the center of the substratebody. In a further implementation, a relatively higher concentration ofthe metal wires is located at some intermediate position between thecenter and perimeter of the substrate body, whereby heat generatedwithin the intermediate layer flows both inwardly towards the center andoutwardly towards the perimeter of the substrate body.

According to another aspect of the invention, an assembly for treatinggaseous emissions comprises a substrate body having a front end, a rearend, a plurality of cells for the passage of emissions gas from thefront end to the rear end, metal located in the substrate body, and aninduction heating coil mounted adjacent the substrate body forgenerating a varying electromagnetic field, thereby inductively to heatthe metal and thereby to heat the substrate body, wherein a greaterconcentration of the metal is located near the front end of thesubstrate body than near the rear end of the substrate body. In oneimplementation, the substrate body has no inductance heating metal nearthe rear end and all of the inductance heating metal is located near thefront end. In such an implementation, the induction heating coil canextend only over a part of the length of the substrate bodycorresponding to the location of the inductance heating metal. The metalcan be configured as wire segments shorter than the full length of thesubstrate body.

According to a further aspect of the invention, an assembly for treatinggaseous emissions comprises a substrate body having a plurality of cellsfor the passage of emissions gas, respective lengths of metal located ineach of a first set of the plurality of cells, and an induction heatingcoil mounted adjacent the substrate body for generating a varyingelectromagnetic field, thereby inductively to heat the lengths of wireand thereby to heat the substrate body, wherein the metal in each of thefirst set of cells is configured as a loop conductor. In oneimplementation, the loop conductors can be a hollow wire.

According to another aspect of the invention, an assembly for treatinggaseous emissions comprises a substrate body having a plurality of cellsfor the passage of emissions gas, respective lengths of metal wirelocated in each of a first set of the plurality of cells, and aninduction heating coil mounted adjacent the substrate body forgenerating a varying electromagnetic field, thereby inductively to heatthe lengths of wire and thereby to heat the substrate body, wherein themetal wires in the first set of cells are joined together to form acontinuous inductance loop conductor.

According to another aspect of the invention, an assembly for treatinggaseous emissions comprises a substrate body having a plurality of cellsfor the passage of emissions gas, respective lengths of metal wirelocated in each of a first set of the plurality of cells, and aninduction heating coil mounted adjacent the substrate body forgenerating a varying electromagnetic field, thereby inductively to heatthe lengths of wire and thereby to heat the substrate body, wherein themetal wires in the first set of cells has one of a hollow cross sectionand an open cross-sectional shape being one a generally L, C, U andV-shape cross-section. In one configuration, at least one of the wiresbears against and covers a part of interior walls of the cell in whichthe wire is contained and leaves another part of the walls of the cellexposed to passage of exhaust gas along the cell, such exposed wall partbearing a layer of pollution treating catalyst. Preferably, a part ofthe wires also exposed to passage of exhaust gas along the cell alsobears a layer of pollution treating catalyst.

According to another aspect of the invention, an assembly for treatinggaseous emissions comprises a substrate body having a front end, a rearend, a plurality of cells for the passage of emissions gas from thefront end to the rear end, respective lengths of metal wire located ineach of a first set of the plurality of cells, and an induction heatingcoil mounted adjacent the substrate body for generating a varyingelectromagnetic field, thereby inductively to heat the lengths of wireand thereby to heat the substrate body, wherein ends of the wiresproject from a front face of the substrate body at the front end. In anexemplary implementation, the induction heating coil extends beyond saidfront face so that a part thereof is adjacent the projecting metal wireends. In operation of the assembly for treating gaseous emissionsdirected into the cells at the front end, the projecting ends can act tobreak up a wave front of the directed gaseous emissions to reduce backpressure. In operation of the assembly for treating gaseous emissionsdirected into the cells at the front end, the projecting ends wheninductively heated can act to pre-heat the gaseous emissions beforeentry thereof into the cells. In one implementation, an inductive spiralloop heating element is also mounted at the inlet face of the substratebody and can be connected to one or more of the projecting metal wireends.

BRIEF DESCRIPTION OF THE DRAWING

For simplicity and clarity of illustration, elements illustrated in theaccompanying figure are not drawn to common scale. For example, thedimensions of some of the elements are exaggerated relative to otherelements for clarity. Advantages, features and characteristics of thepresent invention, as well as methods, operation and functions ofrelated elements of structure, and the combinations of parts andeconomies of manufacture, will become apparent upon consideration of thefollowing description and claims with reference to the accompanyingdrawings, all of which form a part of the specification, wherein likereference numerals designate corresponding parts in the various figures,and wherein:

FIG. 1 is a longitudinal sectional view of a gaseous emissions treatmentunit according to an embodiment of the invention.

FIG. 2 is a cross-sectional view of the gaseous emissions treatment unitof FIG. 1.

FIG. 3 is a perspective sectional view of a part of a gaseous emissionstreatment unit according to an embodiment of the invention showing wireslocated in cells of a substrate body.

FIG. 4 is a representation of an end view of the unit part of FIG. 3showing wires located in a first array pattern and density.

FIG. 5 is a representation of an end view of the unit part of FIG. 3showing wires located in a second array pattern and density.

FIG. 6 is a longitudinal sectional representation of a gaseous emissionstreatment unit according to an embodiment of the invention showing wireslocated in a third array pattern and density.

FIG. 7 is a longitudinal sectional representation showing location ofwire segments for a gaseous emissions treatment unit according toanother embodiment of the invention.

FIG. 8 is a longitudinal sectional representation showing location ofwire segments for a gaseous emissions treatment unit according to afurther embodiment of the invention.

FIG. 9 is a longitudinal sectional representation showing location anddensity of wire segments for a gaseous emissions treatment unitaccording to a further embodiment of the invention.

FIG. 10 is a longitudinal sectional representation showing location anddensity of wire segments for a gaseous emissions treatment unitaccording to yet another embodiment of the invention.

FIG. 11 is a longitudinal sectional representation showing location anddensity of wire segments for a gaseous emissions treatment unitaccording to another embodiment of the invention.

FIG. 12 is a longitudinal sectional representation showing location anddensity of wire segments for a gaseous emissions treatment unitaccording to another embodiment of the invention.

FIG. 13 is an end view of a gaseous emissions treatment unit accordingto an embodiment of the invention.

FIG. 14 is a longitudinal sectional representation of the gaseousemissions treatment unit of FIG. 13.

FIG. 15 is a longitudinal sectional representation showing a two-partgaseous emissions treatment unit according to another embodiment of theinvention.

FIG. 16 is a perspective view of a length of wire for a gaseousemissions treatment unit according to an embodiment of the invention,the wire having incremental changes in properties along the lengththereof.

FIG. 17 is a perspective sectional view of a part of a substrate bodyfor a gaseous emissions treatment unit according to an embodiment of theinvention showing exemplary different forms of wire located in cells ofthe substrate body.

FIG. 18 is a perspective end view of a fragment of substrate body forgaseous emissions treatment unit according to an embodiment of theinvention, the substrate body having a threaded closed loop conductorfor induction heating the substrate body.

FIG. 19 is a longitudinal sectional representation showing a particulatefilter gaseous emissions treatment unit according to an embodiment ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION INCLUDING THE PRESENTLY PREFERREDEMBODIMENTS

A gaseous emissions treatment assembly may take any of a number offorms. Typical of these is a catalytic converter having a cylindricalsubstrate body 10 usually made of ceramic material and often called abrick, an example of which is shown in FIG. 1. The brick has a honeycombstructure in which a number of small area passages or cells 12 extendthe length of the brick, the cells being separated by walls. There aretypically from 400 to 900 cells per square inch (cpsi) ofcross-sectional area of the substrate body 10 and the walls aretypically in the range 0.003 to 0.008 inches in thickness. Typically,the ceramic substrate body 10 is formed in an extrusion process in whichgreen ceramic material is extruded through an appropriately shaped dieand units are cut successively from the extrusion, the units being thencut into bricks. The areal shape of the cells or passages 12 may bewhatever is convenient for contributing to the overall strength of thesubstrate body 10 while presenting a large contact area at which flowingexhaust gases can interact with a hot catalyst coating the interiorwalls of the cells.

The interiors of the tubular cells 10 are wash-coated with a layercontaining a particular catalyst material. A suitable wash-coat containsa base material, suitable for ensuring adherence to the cured ceramicmaterial of the substrate body, and entrained particulate catalystmaterial for promoting specific pollution-reducing chemical reactions.Examples of such catalyst materials are platinum and palladium which arecatalysts effective in converting carbon monoxide and oxygen to carbondioxide, and rhodium which is a catalyst suitable for converting nitricoxide to nitrogen and oxygen. Other catalysts are known which promotehigh temperature oxidation or reduction of other gaseous materials. Thewash-coating is prepared by generating a suspension of the finelydivided catalyst in a ceramic paste or slurry, the ceramic slurryserving to cause the wash-coat layer to adhere to the walls of theceramic substrate body. As an alternative to wash-coating to placecatalyst materials on the substrate body surfaces, the substrate bodymaterial itself may contain a catalyst so that the brick presentscatalyst material at the internal surfaces bounding the cells.

Exhaust gases from diesel (compression combustion) engines contain morenitrogen oxides than gasoline (spark combustion) engines. Long-termexposure to nitrogen oxides even at low levels can cause temporary orpermanent respiratory problems. Selective catalytic reduction (SCR) is amethod by which a liquid reductant is injected into a diesel engineexhaust flow to combine with nitrogen dioxide and nitric oxide (referredto collectively as NO_(X)) in the exhaust gas. A preferred reductant isaqueous urea (2(NH₂)₂CO which is often referred to as diesel exhaustfluid (DEF). In the presence of a catalyst, ammonia resulting fromthermal decomposition of the urea combines with the nitrogen oxides toproduce less harmful products, chiefly nitrogen and water. Otherreductants such as anhydrous ammonia and aqueous ammonia may also beused as an alternative to urea although especially for automotiveapplication, on-board storage presents greater difficulty. Suitablecatalysts may be any of certain metals oxides (such as those ofmolybdenum, vanadium, and tungsten), certain precious metals andzeolites. The typical temperature range for a SCR reaction is from 360°C. to 450° C. with a catalyst such as activated carbon being used tostimulate lower temperature reactions. As in gasoline (spark combustionengines), diesel (pressure combustion) engines may experience a periodafter a start-up where the exhaust temperature is too cool for effectiveSCR NO_(x) reduction processes to take place. Other catalytic convertersin which the present invention finds application for preheating orsupplementary heating are lean NOX catalyst systems, lean NOX trapsystems and non-selective catalytic reduction systems.

A gaseous emissions treatment assembly may have a series of thesubstrate bodies or bricks 10, each having a different catalyst layerdepending on the particular noxious emission to be neutralized. Gaseousemissions treatment bricks may be made of materials other than firedceramic, such as stainless steel. Also, they may have different forms ofhoneycombed cells or passages than those described above. For example,cells can be round, square, hexagonal, triangular or other convenientcross-sectional shape. In addition, if desired for optimizing strengthand low thermal capacity or for other purposes, some of the extrudedhoneycomb walls can be formed so as to be thicker than other of thewalls, or formed so that there is some variety in the shape and size ofcells. Junctions between adjacent interior cell walls can be sharpangled or can present curved profiles.

Typically, as shown in FIG. 1, the wash-coated ceramic honeycomb brick10 is wrapped in a ceramic fibrous expansion blanket 16. A stamped metalcasing or can 18 transitions between the parts of an exhaust pipe (notshown) fore and aft of the gaseous emissions treatment unit so as toencompass the blanket wrapped brick. The casing 18 is typically made upof two parts which are welded to seal the brick in place. The expansionblanket 16 provides a buffer between the casing 18 and the brick 10 toaccommodate their dissimilar thermal expansion coefficients. The metalof the sheet metal casing 18 expands much more than the ceramic materialof the brick at a given temperature increase and, if the two materialswere bonded together or in direct contact with each other, destructivestresses would be experienced at the interface of the two materials. Theblanket 16 also dampens vibrations from the exhaust system that mightotherwise damage the brittle ceramic of the substrate body.

In use, the encased brick (or bricks) is mounted in the vehicle exhaustline to receive exhaust gases from the engine and to pass them to thevehicle tail pipe. The passage of exhaust gases through the gaseousemissions treatment unit heats the ceramic brick to promote catalystactivated processes where the flowing gases contact the catalyst layer.Especially when the vehicle engine is being run at optimal operatingtemperature and when there is substantial throughput of exhaust gases,such treatment units operate substantially to reduce the presence ofnoxious gaseous emissions entering the atmosphere. Such units haveshortcomings however at start-up when the interior of the brick is notat high temperature and during idling which may occur frequently duringcity driving or when waiting for a coffee at a Tim Hortonsdrive-through.

Brick shape, profile and cell densities vary among differentmanufacturers. For example, some bricks are round and some are oval.Some assemblies have single stage bricks that are generally heavilywash-coated with the catalyst metals, while others may have two or threebricks with different wash-coatings on each brick. Some exhausts have900, 600 and 400 cpsi cell densities used in the full exhaust assembly,while others use only 400 cpsi bricks throughout. A close-coupledconverter may be mounted up close to the exhaust manifold with a view toreducing the period between start-up and light-off temperature. Anunderfloor converter can be located further from the engine where itwill take relatively longer to heat up but be relatively larger and usedto treat the majority of gases once the exhaust assembly is up totemperature. In another configuration, a unit for reducing the period tolight-off temperature and a unit to deal with high gas flow afterlight-off are mounted together in a common casing.

At one or more locations in the assembly, sensors mounted in the exhaustgas flow including within or adjacent the substrate body providefeedback to the engine control system for emission checking and tuningpurposes. Aside from start-up, control of fuel and air input has theobject typically of maintaining a 14.6:1 air:fuel ratio for an optimalcombination of power and cleanliness. A ratio higher than this producesa lean condition—not enough fuel. A lower ratio produces a richcondition—too much fuel. The start-up procedure on some vehicles runsrich for an initial few seconds to get heat into the engine andultimately the catalytic converter. The structures and operating methodsdescribed below for indirectly heating the catalyst layers and theexhaust gases can be used with each of a close-coupled catalyticconverter, an underfloor converter, and a combination of the two.Outputs from the temperature sensors are taken to a controller at whichthe monitored temperature or temperatures are used to control wheninduction and/or EHD heating are switched on and off. Using anappropriate algorithm implemented at the controller, the monitoredtemperatures may also be used to control specific effects of the appliedheating processes to achieve a particular heating pattern.

The brick 10 illustrated in the gaseous emissions treatment assembly ofFIG. 1 is modified to enable induction heating. Induction heating is aprocess in which a metal body is heated by applying a varyingelectromagnetic field so as to change the magnetic field to which themetal body is subject. This, in turn, induces eddy currents within thebody, thereby causing resistive heating of the body. In the case of aferromagnetic metal body, heat is also generated by a hysteresis effect.When the non-magnetized ferromagnetic metal is placed into a magneticfield, the metal becomes magnetized with the creation of magneticdomains having opposite poles. The varying field periodically initiatespole reversal in the magnetic domains, the reversals in response to highfrequency induction field variation on the order of 1,000 s to 1,000,000s cycles per second (Hz) depending on the material, mass, and shape ofthe ferromagnetic metal body. Magnetic domain polarity is not easilyreversed and the resistance to reversal causes further heat generationin the metal.

As illustrated in FIG. 1, surrounding the ceramic substrate body is ametal coil 20 and, although not visible in FIG. 1, located withinselected cells 12 are metal rods or wires 22. By generating a varyingelectromagnetic field at the coil 20, a chain reaction is initiated, theend result of which is that after start-up of a vehicle equipped with anexhaust system embodying the invention, light-off may be attained morequickly in the presence of the varying electromagnetic induction fieldthan if there were no such field. The chain reaction is as follows: thevarying electromagnetic field induces eddy currents in the metalelements; the eddy currents cause heating of the metal elements; heatfrom the metal elements is transferred to the ceramic substrate body;heat from the heated substrate body is transferred to exhaust gas as itpasses through the converter; and the heated exhaust gas causes thecatalytic reactions to take place more quickly compared to unheatedexhaust gas. Conduction from the heated wires is the primary source ofheat transfer to the ceramic substrate and therefore to the exhaustgases when the converter is in operation. There is also a small amountof convective and radiated heat transfer at any small air gaps between awire and the interior surface of the cell within which it is contained.

The coil 20 is a wound length of copper tube, although other materialssuch as copper wire or litz wire may be used. Copper tube is preferredbecause it offers high surface area in terms of other dimensions of thecoil; induction being a skin-effect phenomenon, high surface area is ofadvantage in generating the varying field. If litz wire or copper wireis used, an enamel or other coating on the wire is configured not toburn off during sustained high temperature operation of the converter.An air gap between the coil 20 and the nearest inductance metal wires 22prevents significant heat transfer from the wires 22 to the coil 10which would otherwise increase the coil resistivity and so lower itsefficiency.

A layer 24 of electromagnetic field shielding material is locatedimmediately outside the coil 20 to provide induction shielding and toreduce induction loss to the metal converter housing. The shieldinglayer also acts to increase inductive coupling to the substrate body 10to focus heating. The magnetic shield 24 can be made from a ferrite orother high-permeability, low-power-loss materials such as Giron,MagnetShield, Papershield, Finemet, CobalTex, or other magneticshielding material that can arranged to surround some or all of thewindings of the coil 20. In particular, the magnetic shield 24 operatesas a magnetic flux concentrator, flux intensifier, diverter, or fluxcontroller to contain the magnetic fields within the substrate body. Themagnetic shield lowers loss by mitigating undesirable heating ofadjacent conductive materials. Without the magnetic shield, magneticflux produced by the coil 20 could spread around the coil and link withthe electrically conductive surroundings such as the metal casing 18 andother surrounding metal in an exhaust system, and/or other components ofan internal combustion engine, vehicle, generator or other electricalsystem or host system, decreasing the life of these components andincreasing energy loss. In addition, the magnetic shield 24 operates todirect the magnetic field to the substrate body 10 providing selectiveor enhanced heating of a desired region of the substrate body, forexample, by redirecting magnetic flux that would otherwise travel awayfrom that desired region. In particular, the magnetic shield can operateto concentrate the magnetic flux produced by the coil 20 in thedirection of the metal wires or rods 22 in the substrate body 10 formore efficient heating. As an additional benefit, the magnetic shieldcan improve the electrical efficiency of the induction coil 20 byincreasing power transfer.

The coil is contained in a fiber insulation sheath with the sheathedcoil being encased in a in cast, cured insulation. The cast insulationfunctions both to stabilize the coil position and to create an air-tightseal to confine passage of the exhaust gases through the ceramichoneycomb substrate body 10 where catalytic action takes place. Theinsulation also provides a barrier to prevent the induction coil 20 fromshorting on the converter can 18 or the ferrite shield 24. Theinsulation is suitable alumino-silicate mastic. In an alternativeembodiment, the substrate body is wrapped in an alumino-silicate fiberpaper. In one manufacturing method, the copper coil 20 is wrapped aroundthe substrate body and then placed in the casing or can 18. In analternative manufacturing method, the coil 20 is placed in the can 18and the substrate body 10 is inserted into the coil/can assembly.

In one embodiment of the invention, a varying electromagnetic inductionfield is generated at the coil by applying power from either a DC or ACsource. Conventional automobiles have 12 VDC electrical systems. Theinduction system can operate on either DC or AC power supply. Theinduction signal produced can also be either DC or AC driven. For eitherDC or AC, this produces a frequency of 1 to 200 kHz, a RMS voltage of130 to 200V and amperage of 5 to 8 A using 1 kw of power as an example.In one example suitable for road vehicles, a DC to DC bus converts thevehicle's 12 VDC battery power to the required DC voltage outlinedabove. In another example suitable for conventional road vehicles, a DCto AC inverter converts the vehicle's 12V DC battery power to thedesired AC voltage outlined above. Another example is more suited tohybrid vehicles having both internal combustion engines and electricmotors have on-board batteries rated in the order of 360V voltage and 50kW power. In this case, the battery supply power is higher, but the samebasic DC to DC bus or DC to AC inverter electrical configuration can beapplied. An insulated gate bipolar transistor (IGBT) ormetal-oxide-semiconductor field effect transistor (MOSFET) high speedswitch is used to change the direction of electrical flow through thecoil. In terms of the effect of a varying electromagnetic inductionfield on metal in the ceramic substrate body, a low switching frequencyproduces a longer waveform providing good field penetration below thesurface of the metal element and therefore relatively uniform heating.However, this is at the sacrifice of high temperature and rapid heatingowing to the lack of switching. In contrast, a high switching frequencyproduces a shorter waveform, which generates higher surface temperatureat the sacrifice of penetration depth. Applied power is limited to avoidthe risk of melting the metal elements. A suitable power input to asingle brick coil is of the order of 1.1 kw.

As previously described, metal wires or rods 22 are located at selectedlocations of the ceramic substrate body 10 as shown in the detail viewof FIG. 3. The wires 22 are fixed in place by a friction fit which is atleast partially achieved by closely matching the wire exterior areadimensions to the cell area dimensions so that surface roughness of thewire surface and the cell walls 14 locks the wires 22 in place. Wirescan be formed with a non-linear element such as a bow or crimp so thatthe bow or crimp is straightened somewhat as the wire is inserted into acell and so is held by the cell walls as the wire tends to return to itsoriginal bow or crimped shape causing at least a part of the wire tobear against a part of the cell walls 14 and so enhance the friction fitto retain the wire in place. The overall friction fit can be such as toresist gravity, vibration, temperature cycling, and pressure on thewires as exhaust gases pass through the substrate body. Wires mayalternatively, or in addition, be fixed into the cells by bonding outersurfaces of the wires to interior surfaces of respective cells. Asuitable composite adhesive may be a blend of materials chosen to reducetemperature cycling stress effects in which there may be significantmetal wire expansion/contraction, but vanishingly smallexpansion/contraction of the ceramic substrate. This differential canproduce stresses at the adhesive interface between the two materials. Byusing such a composite adhesive, movement of a bonded wire relative tothe surrounding cell walls may be reduced while maintaining high heattransfer.

Field produced by the electromagnetic induction coil (FIGS. 1 and 2) canbe tuned to the metal wire load to achieve high efficiency in terms ofgenerating heat and speed to light-off. Heating effects can be modifiedby appropriate selection of any or all of (a) the electrical inputwaveform to the coil, (b) nature and position of passive flux controlelements, and (c) nature, position, and configuration of the coil. Inparticular, as will presently be described, the heating pattern can bedetermined by appropriate location and configuration of the metal wires.In addition, the applied field can be changed with time so that there isinterdependence between the induction field/heating pattern and theparticular operational phase from pre-start-up to highway driving. In analternative configuration, more than one coil can be used to obtaindesired induction effects. For example, a substrate body having anannular cross-section can have one energizing coil at the substrateperimeter and a second energizing coil at the substrate core (notshown).

A suitable metal for the inserted wire is a ferromagnetic metal such asstainless steel grade 430 which has high magnetic permeability andcorrosion resistance. Lower permeability alloys such as 300 or 400series stainless steels may also be used. Alternative metals can be useddepending on particular properties required in making the wire insertsand in fixing inserts within selected cells of the ceramic substrate.Such properties include metal formability, ductility, softness andelasticity. For shaping the direction and strength of magnetic flux inthe substrate, lower magnetic permeability metals or alloys may be usedfor metal inserts in the outer cells with relatively higher magneticpermeability metals being used for metal inserts in the inner cells.Metals having very high magnetic permeability may also be used. Forexample, Kanthal iron-chrome-aluminum alloys used in wires manufacturedby Sandvik have a relative permeability of 9000 and greater. Highrelative permeability can be achieved using wires made of other alloysincluding nickel-iron and iron-cobalt alloys.

In the embodiments of FIGS. 4 and 5 which show in each case a small partof a substrate body 10, the wires 22 are arranged in a regular array asviewed from one end of the substrate body or in cross-section across it.In FIG. 4, there is a metal wire at every 5^(th) cell viewed verticallyand horizontally (1:25). In FIG. 5, there is a metal wire at every7^(th) cell viewed vertically and horizontally (1:49). Other operatingparameters being equal, the 1:49 array has higher flux density than the1:25 array as there are fewer wires. Flux density is generally moreevenly distributed in the 1:25 array than the 1:49 array. Otheroperating parameter being equal, the 1:49 array produces more heat thanthe 1:25 array. A 1:25 array in a 400 cells per square inch (cpsi)substrate has a satisfactory heating performance and not too great anocclusion of converter cells from the viewpoint of pollution-cleaningcatalytic reactions implemented when operated as a catalytic converteror PF. A significantly higher ratio of wires to cells can result inslower heating to light-off because of the high overall thermal capacityrepresented, in total, by the wires and because of the fact that somewires block the “line of sight” field effect on other wires. Incontrast, while a significantly lower ratio of wires to cells results infewer occlusions of converter cells, a sparse distribution of metalresults in reduced heat generation and increased time to light-off.

A uniform wire array such as those shown in FIGS. 4 and 5 will notnormally produce uniform heating or a uniform temperature through thesubstrate body although it may provide rapid heating and a generallyuniform temperature profile for smaller substrate bodies, typically 4inches in diameter or less, because, in that case, all wires arerelatively close to the coil. Such a small substrate body may be usedfor small displacement gasoline engines. For substrate bodies largerthan 4 inches in diameter, induction heating from a uniform wire arraypattern has lower electrical and thermal efficiency. Because magneticflux from the coil is strongest closest to the coil and weakens furtheraway from the coil, a metal wire closer to the source of the inductionfield becomes hotter and becomes hot more quickly than an equivalentmetal wire located further away from the source. In such substratebodies, the magnetic flux is not as uniform as in the smaller substratebodies. Center and outer located wires do not experience similar levelsof magnetic flux as the magnetic flux drops off drastically withdistance from the coil.

As shown in FIG. 3, the interior walls 14 of the cells 12 are coatedwith a catalyst 15 if the assembly is to function as a catalyticconverter but may be uncoated or coated if the assembly is to functionas a particulate filter.

In alternative embodiments as shown in FIGS. 6 to 10, the distributionof metal wires 22 is shown, but not the substrate body itself or otherelements of the gaseous emissions treatment assembly such as anycatalyst coating, coil and casing.

As shown in FIG. 6, a relatively higher concentration of metal wires 22(wires per unit volume) is sited towards the center of the substratebody to compensate for the fact that the field effect from the coilsource will be considerably less near the center 26 of the substratebody than near the outer part 28. The FIG. 6 embodiment has closelyspaced wires near the center 26 and also at an intermediate position 30.More or less complex wire placement configurations can be adopteddepending on the temperature profile and heat flow patterns desired. Theabsence of wires at outer region 28 of the substrate body 10 limits thenumber of preferred inductance paths at the outer regions. This forcesmagnetic flux to find the next best preferred inductance path which, inthe absence or scarcity of wires in the outer region 28, will be a wireor wires closer to the center 26 of the substrate body. Flux, andtherefore heat, are consequently guided towards the center of thesubstrate body. This results in the center section 26 being adequatelyheated and, just as importantly, the outer regions 28 not beingoverheated. The densest array of wires 22 is found at the center 26 ofthe substrate body 10 and the lowest density is found in the outerregion 28. There may be a progressive change in the array patterndensity or a stepped change with defined array densities in specificregions such as the center, middle and outside.

In the previously described embodiments, the distribution of inductancemetal elements 22 relative to the positions of the cells 12 isconfigured so that the heating effect is generally uniform across thearea of the substrate body 10. Especially for start-up and idling, wherenon-uniform exhaust gas flow patterns may develop, there may beadvantage in developing a heat pattern across the substrate body whichis not uniform. As previously noted, this may be achieved byappropriately siting inductance metal wires or rods 22 in selected cells12. It may also be achieved in another embodiment of the invention byusing differently sized, shaped or composition metal wires.

In the embodiments illustrated in FIGS. 7 to 10, wire segments 32 extendalong part only of the lengths of selected cells 14, the lengths andpositions of the wire segments 32 being selected to shape the fluxdensity pattern and heating effect.

In the FIG. 7 embodiment, there are two wire segments 32 in each of theselected cells towards the outside 28 of the substrate body but singlelong wires 22 in selected cells near the core 26 of the substrate body.As in the case of full length wires, the closest wire segment 32 marksthe preferred inductance path for magnetic flux. Flux traveling along awire segment 32 will therefore tend to jump across a short air gap tothe next closest neighboring wire segment 32 rather than travel througha long air gap. To encourage movement of the magnetic flux towards thecenter 26 of the substrate body 10, as shown in FIG. 7, a gap ‘g’between wire segments 32 occupying the same cell 12 in the outer region28 is made greater than the gap between wire segments occupying the cell12 next closer to the center of the substrate body. The outside wiresegments are made the shortest because they are closest to the inductioncoil and therefore experience the highest magnetic flux. The segmentslengthen towards the center 26 of the substrate body to the point wherefull length wires are used in the center region 26 of the substrate body10. This spreads the magnetic flux and therefore the heating effect muchmore effectively throughout the substrate body.

In the FIG. 8 embodiment, each selected cell contains only one wiresegment 32 or a full length wire for centrally located cells. However,similarly to the FIG. 7 embodiment, wire segments 32 in selected cellsnear the outside 28 of the substrate body 10 are shorter than wiresegments 32 in selected cells near the core 26 of the substrate body. Inthis case, the high concentration of wire is at the front end 36 of thesubstrate body 10; i.e. the end at which, in operation, emissions gases38 enter the gaseous emissions treatment assembly, as compared with themetal wire concentration located at or near the rear end 40 of thesubstrate body where treated emissions gases 42 exit the assembly.

In a particular variation as shown in FIGS. 11 and 12, the wires or rods22 are concentrated at the front end but with no wires and no part ofthe coil 20 located beyond a certain downstream position. With such adesign, generation of electromagnetic flux and heating is focused at thefront end of the brick. For a given power input, this enables a smallpart of the brick substrate to be heated quickly to a desired light offtemperature instead of having the full brick heated more slowly, theheated part being that part first encountered by exhaust gases 38entering the system. Front end induction heating of the substrate body10 can produce a cascade effect if the heated front end acts to igniteunburned hydrocarbons in the exhaust gas entering the assembly duringoperation before light off is reached or during idling. The burninghydrocarbons as they pass down the substrate body 10 hasten the rate atwhich the downstream part of the substrate body and the catalyst layerreach the light off temperature whether or not that downstream part isbeing is being directly inductively heated.

For improved thermal performance, the FIGS. 4, 5 and 6 (wireconcentration positioning) and the FIGS. 7 and 8 (wire segment position)design methods for shaping magnetic flux density through the substratebody can be combined as illustrated in FIGS. 9 and 10. There can be anadded benefit through using the greater wire-to-wire spacing of thevariable array pattern in conjunction with wire segments 32 extendingonly part way along the lengths of the cells in which they arecontained. Thus, appropriately configured, more magnetic flux can bemoved to the center of the substrate body to produce a variety ofheating effects. Uniform heating is possible by using variable wiresegment lengths distributed symmetrically front to back in the substratebody. More intense heating on one face of the substrate body can beachieved by distributing the wire segments asymmetrically front to back.The region with the highest concentration of wire segments willexperience more heating. Intense heating in the center is possible byremoving more outside wires and shortening the wire segments whichallows more magnetic flux to reach the center and therefore produce moreheat. Intense heating in the dead center and very little on the facesand outer regions is possible by shortening the wire segment lengths inthe center and reducing the number of wires in the outer region.

Catalytic reactions that take place at and above the light-offtemperature are exothermic. Heat energy produced acts to raise thetemperature of the substrate body above that which would be achieved bythe exhaust gas alone. The exothermic reaction is self-fuelling in that,above light-off and with an adequate flow-through of exhaust gas, theexothermic reactions produce an increase of catalyst temperature by upto 100° C. As a corollary, if the flow-through of hot exhaust gas fallsbelow that which is necessary to maintain the catalyst at the light-offtemperature, the exothermic reactions cease.

FIG. 1 shows the substrate body being heating relatively uniformly alongits length. In another embodiment of the invention, variations of whichare depicted in FIGS. 11 to 15, induction heating is applied only to afront end part of the substrate body which, in some circumstances, canoffer an advantage compared to uniform heating along the length of thesubstrate body. In explanation, firstly, if inductive heating is appliedbefore or immediately after engine start, some of that heat will be lostfrom the catalyst regions both through conduction and radiation awayfrom the heated zones and from convection owing to the still-coldexhaust flowing through the cells. The exhaust gas flow may push heatout of the back of the substrate body before light-off is achieved sothat heat is lost from the system. Secondly, if a particular inductionpower is concentrated over only a small volume of the substrate bodylength instead of its full length, a higher flux density and a greaterheating effect is produced over that smaller volume and the focusedheating starts the previously described exothermic reactions earlierthan if that power were applied over the full substrate body length.Thirdly, heating the whole substrate body requires a greater mass ofmetal heating elements, a longer induction coil, and greater mass ofmagnetic flux concentrator compared with materials needed for smallvolume heating and this adds cost and complexity.

Referring in detail to FIG. 11, a wire pattern is used that heats onlythe front one third of the substrate body. One suitable wire arrayprofile is the illustrated asymmetric D-shaped profile although othersymmetric or asymmetric array profiles may function equally well. TheD-shaped profile array contains wire segments 32 having a range oflengths with the longest wires in the middle and the shortest at theouter edges. This profile distributes the magnetic flux well. Typically,the longer wires in the center can be almost half the length of thesubstrate body with the outer wires being about one-third of the lengthof the center wires. The average volume that the D-shaped profileoccupies is about one-third of the length of the substrate body orequivalent to about one-third the volume.

In the embodiment of FIG. 12, a symmetric D-form or other suitable wirearray profile has wires 44 protruding from the front 36 of the substratebody. In operation, the heated protruding wire ends 44 heat exhaust gas38 directly as it flows into the respective cells. Because there is nopart of the substrate body surrounding the wire protrusions 44, the heatgoes straight to the exhaust gas 38 and not indirectly via the substratebody 10. This slightly improves the efficiency and time to light-off.The protrusion distance is limited to that required in order for thewire to be stable and not easily deform under heat and vibration. Thecoil and magnetic flux concentrator (not shown) are translated forwardto match the positions of the protrusions 44.

In the embodiment of FIGS. 13 and 14, a spiral loop inductive heatingelement 46 is positioned near the inlet face 36 of the substrate body 10and acts in use to preheat exhaust gas 38 before it enters the cells ofthe brick. Ends of the heater element located respectively at the centerand outer extremity of the spiral are connected together by a linksection to close the loop. Here, the majority of inductively generatedheat in the spiral heater is transferred directly to the exhaust gas.Wire protrusions or spurs 48 from the upstream heater element 46 arelodged into the ends of corresponding cells 22 of the substrate body 10to lock the heater element 46 onto the front face 36 of the substratebody. The element 46 is positioned at least one wire diameter or about 1to 5 mm away from the front face 36 of to avoid blocking the entrancesto cells 12 beyond that needed to support the heating element. Certaincells of the substrate body may contain heating wires to complementand/or focus heating by the spiral loop heating element.

In the embodiment of FIG. 15, an inductively heated catalyst unit 50 ispositioned immediately upstream and physically separated from a maincatalyst unit 52. Decoupling an inductively heated front end unit 50from a rear catalyst unit 52 obviates stresses and strains caused byrapid expansions and contractions of the substrate body materialcompared to an arrangement where the two zones are present in the samesubstrate body. Decoupling allows the two substrates to actindependently so that one can expand or contract rapidly withoutimpacting the other.

In each of the embodiments of FIGS. 11 to 15, the length and shape ofthe wires 22 and segments 32 in the front-end located wire array can betuned for the desired heating level and distribution. In addition, forall embodiments described in this specification, heat transfercharacteristics of the material of the substrate body 10 also influencethe heating effect and therefore must be considered when selecting thelocations of the wires or wire segments. For example, cordierite andsilicon carbide are suitable materials for the substrate body, withcordierite having a relatively low heat transfer coefficient and siliconcarbide having a relatively high heat transfer coefficient. As a result,silicon carbide can be provisioned with fewer heating wires thancordierite for the same heating effect.

As an alternative to shaping the magnetic field and heating effect usingwire segments 32 and air gaps ‘g’, the gaseous emissions treatment unitcan alternatively be implemented using metal wires where one wire or rodmay have inductance properties different from another wire. In one suchimplementation, the magnetic permeability of wires positioned near theoutside of the substrate body is lower than the magnetic permeability ofwires positioned near the inside of the substrate body so as todistribute the magnetic flux as desired. In one example, wires near thecenter of the substrate body are made of 430 stainless steel and wiresnear the outside of the substrate body are made of 409 stainless steel.

In another implementation, as illustrated in FIG. 16, the permeabilityof a wire 22 varies along its length, the variation, for example, beingin stepped discrete increments 54. By appropriately adjusting thepermeability of a wire along its length, it can be made to have the sameeffect as wire segments separated by an air gap where there is nopermeability difference between the metal of the two segments.Generally, for inductive heating of the substrate body containing suchwires, higher permeability materials are placed in areas where greaterheating is required and lower permeability materials where less heatingis required. Establishing a variation in magnetic permeability along awire is effected by differential heat treatment (annealing andquenching) at different regions of the wire. These processes change themicrostructure which in turn sets the related magnetic permeability.Alternatively, or in addition, wires are permanently magnetized bysubjecting them to a magnetic field with, for example, one part of awire being magnetized more than another part. In operation, magnetichysteresis differences between the separate parts of the wire influencethe flux and heating pattern/effect. The resistivity of a metal wirealso affects the way in which it is heated in the presence of a varyingmagnetic flux and therefore to obtain a desired differential response tothe flux, the magnetic permeability and resistivity of the differentwire regions must be considered together.

Whether a wire extends the full length of a cell or only partially alongits length, the particular occupied cell is rendered compromised orunusable in terms of promoting a catalytic reaction to remove noxiouscomponents of exhaust gas passing through the catalytic converter or PF.This adverse effect can, in an alternative embodiment, however, bemitigated to some effect by using non-solid wires.

A hollow wire 56 such as that shown in upper cell 23 illustrated in FIG.17, presents a closed loop circuit parallel to the loops of theinduction coil. Generation of eddy currents in wire conductors is asurface effect so that a majority of current flow is at the surface of awire 22 compared with current flow in the core of the wire. However,because current is not confined at the surface of a solid conductor, thesurface eddy currents tend to dissipate somewhat as current flows fromthe surface towards and through the core of the wire. By using hollowwires 56, the surface area at which eddy currents are generated iseffectively doubled because the hollow wire has both an outside surface58 and an inside surface 60. In addition, by confining current flow to aclosed loop, current is prevented from flowing to the axis of the wire56 so that for the duration of time that a particular eddy currentexists, its current flow is retained near the surface of the wire whereit can have the greatest heating effect. The combined effect is greatersurface current flow and increased heating at the wire conductorsurfaces. An advantage of the hollow wire 56 in comparison with a solidwire is that the former does not completely block or occlude thecatalytic converter or PF cell in which it is contained and so allowsexhaust gas to pass through the cell while still functioning as aheating element. Consequently, other design parameters being equal,system back pressure is reduced compared with the use of solid wires.Reducing back pressure is important because back pressure reduces engineperformance. In one example, a hollow wire that is 50% open has aninside diameter that is 70.7% of the outside diameter. This translatesto 50% less back pressure for the same number of solid wires. For 75%open, four times as many hollow wires can be used compared with solidwires for the same back pressure. Non-circular hollow profiles such assquare, triangular and hexagonal can also be used. Both the interior andthe exterior of the hollow wire 56 can be coated with a catalyst forpromoting or accelerating gaseous emissions treatment reactions with thecatalyst being applied to the wire either before insertion into therespective cell 12 or being applied to the substrate body and wiresafter the wires have been inserted into their respective cells. In someinstances catalyst metals may be alloyed with the metal of the wire topresent catalyst at the wire surface. Alternatively, catalyst metalliclayers are deposited by chemical vapor deposition or like process.

In a further variation, as shown in the lower cell 25 illustrated inFIG. 17, an L-section wire 61 positioned in the square cell 25 is usedto heat two side walls 14 of the cell, with the other parts of the cell,including the other two walls, being open to present a significant areaof catalyst to exhaust gas flowing along the cell. With a change fromsolid wire cross-section to non-solid wire cross-section (includingactual hollow, L, C, U, V and like open form shapes), the inductionfield absorption characteristics also change. With a thinnercross-section compared with a solid wire, a higher induction coilswitching frequency is used so as to shorten the penetration depth intothe wire, to thereby match the reduced thickness and, in turn, toincrease thermal conversion efficiency.

For a catalytic converter, exhaust gas passing down the center of ahollow wire conductor does not impinge on catalyst because it isseparated from the coated substrate cell walls by the hollow wireconductor walls. Consequently, absent coating of the hollow conductors,untreated exhaust gas would pass down the interior of the hollowconductors without emissions treatment. To counter this, either theceramic substrate body is coated with catalyst after the hollow wiresare inserted or the hollow wires are coated with catalyst and theninserted into the coated ceramic substrate. For a conducting hollow wiresegment that is relatively short, once exhaust gas has passed along thesegment and enters an unoccupied length of the cell, the exhaust gas issubject to the effect of the exposed catalyst layer to stimulate hightemperature emissions treatment. By using hollow wires segments ofappropriate length and position, the amount of blocked cells can bereduced from 3% for a 1:25 solid wire design down to 0% with an almostnegligible increase in back pressure for a 1:25 hollow wire design. Onepotential issue with a hollow wire is ensuring enough mass for effectiveheat transfer. Optimum wall thickness for a hollow wire is based on thepenetration depth of the induction field. The hollow wire wall shouldnot be so thin that it is essentially transparent to the magnetic fluxin terms of developing eddy currents and associated heating, However, itshould not be so thick that a significant amount of eddy currentgenerated at the wall surfaces is quickly lost to the interior.

In another loop configuration as shown in FIG. 18, a single wire 62 isthreaded backwards and forwards through selected cells 22 in thesubstrate body, the ends of the wire being joined together to close theloop. In effect, adjacent wire inserts in the selected channels arestitched into place. The closed loop configuration ensures substantiallythe same level of current anywhere in the loop at a given timeregardless of positional variation in magnetic flux because current flowin the closed loop tends to normalize any current gradients that mimicflux gradients. In turn, the consistent current effectively translatesto consistent wire temperature.

As previously mentioned, the induction heating configurations previouslydescribed and illustrated can be used with both catalytic converters andparticulate filters (PFs). A PF is a device used in motor vehicles andother applications for removing particulate matter from the exhaust gasof an engine. The particulate matter includes ash, soot and otherparticulate material resulting from incomplete combustion of the enginefuel/air mix. Unlike a catalytic converter which is a flow-throughdevice, a PF captures exhaust gas particles by forcing the exhaust gasthrough a filter medium. PFs have been widely commercially adopted fordiesel (compression combustion) engines. Several types of PF have beenused including cordierite wall flow filters, silicon carbide wall flowfilters, ceramic fiber filters and metal fiber flow-through filters. PFsare also being increasingly commercially adopted for gasoline (sparkcombustion) engines. PFs may have a catalyst component to reduceemissions of noxious components or may be standalone with a PF unitextracting particulate matter and one or more catalytic converterslocated at other locations along the exhaust gas route convertingharmful emissions substances to less harmful materials.

One form of PF has a ceramic substrate of honeycomb form having a largenumber of cells or passages extending from an input end to an output endof the filter. Alternate cells are blocked on the entrance face of thefilter with fired plugs of ceramic of the same base material as theextruded substrate. Intermediate cells are blocked at the exit face ofthe filter so that a chequered pattern is present at each end of thesubstrate. In use, exhaust gas from the engine enters the cells that areopen at the PF input end. The exhaust gas is forced through cell wallsinto the adjacent cells that are open at the PF output end. However,particles of ash or soot are retained on the cell walls, with only verysmall particles occasionally passing through the walls.

Over time, soot and ash particles from the exhaust gas flow through thePF tend to build up and start to block the pores of the filter medium.To prevent the PF from becoming inefficient or inoperative, theaccumulated particles are periodically burned off. In one method, thisis done using a regeneration cycle in which introduced regeneration fuelis burned to heat the filter to a temperature at which the sootcombusts, the PF reaching a temperature somewhat higher than thatreached during normal engine operation. Typically, a particulate filterregenerates at a temperature between 500 to 700 degrees C. depending onparticular system factors. Only under very high RPM and loads would aconventional automobile engine attain a temperature of that order.Consequently, in a PF regeneration operation, fuel is injected to raisethe exhaust temperature. The temperature of a PF during a fuel burnregeneration cycle may be reduced somewhat by using a catalyst combinedwith the introduced regeneration fuel. A diesel engine (compressioncombustion) fuel air mix has a high oxygen content compared with agasoline (spark combustion) engine fuel air mix and the high diesel fueloxygen content can facilitate the fuel burn cycle. Timing and othercontrol aspects of the regeneration cycle are controlled by the on-boardcomputer used to control engine function, the computer working inconjunction with multiple sensors and control inputs associated with thePF.

Referring to FIG. 19, in another embodiment of the invention, anexemplary induction heated particulate filter (PF) 64 is shown, thefigure showing solely a part of the substrate body 11 and the outercasing 18. In comparison with a standard PF, some or all of cells 66that are blocked at the input end of the substrate body 11 are blockedwith metal wires 68 instead of the conventional ceramic plug. The metalwires 68 act to block the particular cells 66 so that the desired flowof exhaust gas through walls 70 of the substrate body 11 is achieved. Inaddition, the metal wires 68, when subject to a varying electromagneticfield, also function as local heaters. As shown in FIG. 19, metal wireplugs 68 in certain cells have lengths different from metal wire plugsin other cells. In one embodiment, metal wire plugs 72 near the outerpart of the substrate body 11 are shorter than metal wire plugs 74 nearthe center of the unit to guide magnetic flux towards the core of thesubstrate body 11. The PF heating of the metal wire plugs 68 can beactuated during a fuel burn as a contributory part of heating during aregeneration cycle or can be used to preheat the PF so that, in bothcases, less fuel need be injected during the fuel regeneration burnitself. If sufficient heat is generated by the induction heating, theuse of extra fuel for the regeneration heating cycle may be obviatedaltogether.

In a fuel regeneration process, hot exhaust gases are generated some wayupstream of the PF and may lose significant heat in the course offlowing to the PF from the engine. In contrast, the induction heatingelements 68 are located within the substrate body 11 at its upstreamside, so that the induction heat generated is immediately and directlyused to heat the walls 70 of the PF with some of that heat beingtransferred along the length of the PF by a combination of radiation,convection and conduction.

As further illustrated in FIG. 19, all or some of the metal plugs at theinput end of the PF unit can have surfaces that are flush with an inputface of the unit as illustrated by metal plugs 68. Alternatively, someor all of the metal plugs can have end portions 76 protruding forwardlyof the face 78 of the unit as shown by plugs. Inevitably, exhaustbackpressure is generated at the PF unit because of the blocked cells.The back pressure causes a drop in engine performance and fuel economy.It is desirable to increase back pressure as little as possiblecommensurate with the PF unit effectively performing its exhaustemissions treatment. In use, when an exhaust stream 38 is direct throughthe exhaust pipe assembly against the input face 78 of the emissionstreatment unit, the wire protruding heads 76 act to break up thepressure wave tending to build up at the face 78 of the substrate bodywhere the exhaust impinges before flowing into the substrate body 11 andthrough its walls 70. The pressure wave front is caused to break upowing to the wave front encountering the wire protrusions 76 beforeencountering the input face 78 of the substrate body 11. Breakup of thewave front reduces the back pressure that the ceramic presents to theexhaust system which, in turn, increases exhaust gas velocity throughthe exhaust emissions unit.

Selection of the length of protrusion from the ceramic substrate frontface 70 depends on several factors including cell density (cpsi) of thesubstrate body, wire array pattern, exhaust gas velocity and the wirediameter/cross-sectional area. In one embodiment of the invention theprotrusion length is from one wire diameter upwards with a longerprotrusion length corresponding to faster exhaust gas velocities.However, the protrusion length is not made so long that the broken upwave front will re-establish before the pressure wave impinges on theface of the input face of the ceramic substrate. Furthermore, theprotrusion length is not made so long that there is a risk of theunsupported wire end bending at high temperature such as thatexperienced, for example, during a regeneration burn. Althoughillustrated for a PF in FIG. 19, metal inserts for catalytic converterscan also be configured to protrude from the ceramic brick front surfacefor the same wave front breaking purpose. In addition, as furtherillustrated in the FIG. 19 PF, supplementing the effect of theprotruding metal plugs, some or all of any ceramic plugs 88 at theleading end 78 of the unit can also be formed to have a wavefront-breaking shape. The metal inserts for a catalytic converter ormetal inserts or ceramic plugs for a PF can have protruding parts 76with a curved or pointed profile as shown at 82 so as further to reduceback pressure.

One example embodiment of the invention had the following structuralcharacteristics and performance:

-   -   a cordierite honeycomb substrate body with 900 cpsi, 4.66 inches        diameter and 3.75 inches length    -   a 1:25 wire array pattern front-end loaded D-shaped profile    -   total system weight (excluding case shielding, flux        concentrator, etc.) of 523 grams made up of 454 grams of        washcoated ceramic honeycomb with 67 grams of wire and 2 grams        of mastic adhesive    -   inductance with a 19 turn coil: 48 uH    -   center temperature (1.5 inches from front face): 308° C. after        150 seconds at a frequency of 100 kHz for a 1.2 KW power draw

Another example embodiment of the invention had the following structuralcharacteristics and performance:

-   -   a cordierite honeycomb substrate body with 400 cpsi, 5.66 inches        diameter and 3.75 inches length    -   a 1:25 wire array pattern full length symmetric profile    -   total system weight (excluding case shielding, flux        concentrator, etc.) of grams made up of 750 grams of washcoated        ceramic honeycomb with 150 grams of wire and 5 grams of mastic        adhesive    -   inductance with a 15 turn coil: 64 uH    -   center temperature (1.75 inches from front face): 140° C. after        150 seconds at a frequency of 87 kHz for a 1.2 KW power draw

Other variations and modifications will be apparent to those skilled inthe art and the embodiments of the invention described and illustratedare not intended to be limiting. The principles of the inventioncontemplate many alternatives having advantages and properties evidentin the exemplary embodiments.

What is claimed is:
 1. An assembly for treating gaseous emissionscomprising a substrate body having a front end, a rear end, a pluralityof cells for the passage of emissions gas, inductance heating metallocated in the substrate body, and an induction heating coil mountedadjacent the substrate body for generating a varying electromagneticfield, thereby inductively to heat the metal and thereby to heat thesubstrate body, wherein a greater concentration of the metal is locatednear the front end of the substrate body than near the rear end of thesubstrate body.
 2. The assembly of claim 1, wherein the inductanceheating metal is respective lengths of metal wire located in each of afirst set of the plurality of cells
 3. The assembly of claim 1, wherein,the inductance heating metal is confined to a front part of thesubstrate body and the induction heating coil is mounted adjacent only afront part of the substrate body.
 4. The assembly of claim 2, wherein atleast some of the lengths of metal wire are wire segments shorter thanthe full length of the substrate body.
 5. The assembly of claim 2,wherein end portions of the lengths of wire project from a front face ofthe substrate body at the front end.
 6. The assembly of claim 5, whereinthe induction heating coil extends beyond said front face so that a partthereof is mounted adjacent the projecting wire end portions.
 7. Theassembly of claim 5, wherein the projecting wire end portions tapertowards the ends of the wires.
 8. The assembly of claim 5, wherein atleast two of the projecting wire end portions are joined to each otherby a spiral heating element which element is mounted in front of thefront face for inductive heating thereof by the induction coil.
 9. Theassembly of claim 4, there being a greater concentration of wire perunit volume of the substrate body towards the center of the substratebody than at the perimeter thereof.
 10. The assembly as claimed in claim5, wherein wire segments are located at the front of the substrate bodybut not at the back of the substrate body, the induction heating coilmounted adjacent the substrate body at the front of the assembly. 11.The assembly as claimed in claim 5, wherein wire segments in a firstsubset of the first set of cells are longer than wire segments in asecond subset of the first set of cells.
 12. The assembly as claimed inclaim 2, the metallic composition of one wire being different from themetallic composition of at least one other wire.
 13. The assembly asclaimed in claim 1, the substrate body made of a ceramic honeycombmaterial.
 14. The assembly as claimed in claim 1, the metal being aferromagnetic metal.
 15. The assembly as claimed in claim 1, the wireshaving one of a hollow and an open cross-section configuration.
 16. Aprocess for treating gaseous emissions using an assembly having aninduction coil mounted adjacent a substrate body, the substrate bodyhaving a plurality of cells for the passages of emissions gas,inductance heating metal located in the substrate body with a greaterconcentration of the inductance heating metal being located near thefront end of the substrate body than near the rear end of the substratebody, and an induction heating coil mounted adjacent the substrate body,the method comprising generating a varying electromagnetic field thecoil thereby to cause induction heating of the metal, heat from theheating metal being transferred to the substrate body and to gaseousemissions passing along the cells, the heating being greater at thefront end of the substrate body than at the rear end thereof.
 17. Theprocess as claimed in claim 16, walls of the cells having catalystsurface layer, the induction heating acting to heat the layer to promotea catalytic reaction in the gaseous emissions passing along the cells18. The process as claimed in claim 17, the catalytic reaction being anexothermic reaction.
 19. the catalytic inductively to heat the metal andthereby to heat the substrate body and thereby heating gaseous emissionspassing along the cells, y, the electromagnetic field generationoperable inductively to heat the lengths of wire, thereby to heat thesubstrate body and thereby to heat emission gases passing along thecells, the location of the wires distributed non-uniformly through thesubstrate body to obtain a desired heating pattern in the substratebody.
 20. A process for treating gaseous emissions, at least some of themetal wires and the cells within which the wires are contained having asurface layer of catalyst material for treating emissions gas passingthrough the cells, the method comprising varying an electromagneticfield generated by the induction heating coil inductively to heat thelengths of wire, thereby to heat the substrate body and thereby to heatthe emission gases passing along the cells, gaseous emissions passingalong at least one of the cells being subject to catalyst promotedreactions at both walls of the cells and the surface of the wirecontained in the cell.
 21. An assembly for treating gaseous emissionscomprising a substrate body having a front end, a rear end, a pluralityof cells for the passage of emissions gas, inductance heating metallocated in the substrate body, and an induction heating coil mountedadjacent the substrate body for generating a varying electromagneticfield, thereby inductively to heat the metal and thereby to heat thesubstrate body, wherein a greater concentration of the metal is locatednear the front end of the substrate body than near the rear end of thesubstrate body.
 22. The process as claimed in claim 16, furthercomprising generating the varying electromagnetic field when an enginewhich is the source of the emission gases is operating and when thesubstrate body is below a predetermined threshold temperature.
 23. Theprocess as claimed in claim 16, further comprising generating thevarying electromagnetic field for an engine which is to be the source ofthe emission gases before start-up of the engine.
 24. The process asclaimed in claim 16, further comprising inductively preheating gaseousemissions before the gaseous emissions enter the substrate body.